mdmon: already read sysfs files once after opening.

seq_file in the kernel will allocate a read buffer on
first read.  We want this to happen under the managemon thread,
not the 'monitor' thread, as the latter is not allow to allocate
memory (might deadlock).
So do a first read after opening.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 23 insertions, 7 deletions

diff --git a/managemon.c b/managemon.c
index 1c9eccc..9b14d1e 100644
--- a/managemon.c
+++ b/managemon.c
@@ -402,6 +402,20 @@ static void manage_container(struct mdstat_ent *mdstat,
 	}
 }
 
+static int sysfs_open2(char *devnum, char *name, char *attr)
+{
+	int fd = sysfs_open(devnum, name, attr);
+	if (fd >= 0) {
+		/* seq_file in the kernel allocates buffer space
+		 * on the first read.  Do that now so 'monitor'
+		 * never needs too.
+		 */
+		char buf[200];
+		read(fd, buf, sizeof(buf));
+	}
+	return fd;
+}
+
 static int disk_init_and_add(struct mdinfo *disk, struct mdinfo *clone,
 			     struct active_array *aa)
 {
@@ -409,10 +423,11 @@ static int disk_init_and_add(struct mdinfo *disk, struct mdinfo *clone,
 		return -1;
 
 	*disk = *clone;
-	disk->recovery_fd = sysfs_open(aa->info.sys_name, disk->sys_name, "recovery_start");
+	disk->recovery_fd = sysfs_open2(aa->info.sys_name, disk->sys_name,
+					"recovery_start");
 	if (disk->recovery_fd < 0)
 		return -1;
-	disk->state_fd = sysfs_open(aa->info.sys_name, disk->sys_name, "state");
+	disk->state_fd = sysfs_open2(aa->info.sys_name, disk->sys_name, "state");
 	if (disk->state_fd < 0) {
 		close(disk->recovery_fd);
 		return -1;
@@ -692,11 +707,12 @@ static void manage_new(struct mdstat_ent *mdstat,
 		}
 	}
 
-	new->action_fd = sysfs_open(new->info.sys_name, NULL, "sync_action");
-	new->info.state_fd = sysfs_open(new->info.sys_name, NULL, "array_state");
-	new->resync_start_fd = sysfs_open(new->info.sys_name, NULL, "resync_start");
-	new->metadata_fd = sysfs_open(new->info.sys_name, NULL, "metadata_version");
-	new->sync_completed_fd = sysfs_open(new->info.sys_name, NULL, "sync_completed");
+	new->action_fd = sysfs_open2(new->info.sys_name, NULL, "sync_action");
+	new->info.state_fd = sysfs_open2(new->info.sys_name, NULL, "array_state");
+	new->resync_start_fd = sysfs_open2(new->info.sys_name, NULL, "resync_start");
+	new->metadata_fd = sysfs_open2(new->info.sys_name, NULL, "metadata_version");
+	new->sync_completed_fd = sysfs_open2(new->info.sys_name, NULL, "sync_completed");
+
 	dprintf("%s: inst: %s action: %d state: %d\n", __func__, inst,
 		new->action_fd, new->info.state_fd);